Method of producing tough breathable coating of polyurethane on fabrics



United States Patent US. Cl. 117-65.2 7 Claims ABSTRACT OF THE DISCLOSURE Breathable coated fabrics wherein the coating is thermoplastic polyurethane are toughened by applying heat and pressure to the breathable coating to reduce the thickness to 40 to 60% of its original thickness. The toughened coated fabric is especially useful as a leather substitute material.

This application is a continuation-in-part of U5. Ser. No. 550,135, filed May 16, 1966, and now abandoned.

This invention relates to water vapor permeable coatings having a moisture vapor transmission comparable to that of leather, and aims to provide tough breathable coatings of polyurethane on textile fabrics.

This invention represents an improvement of the invention covered in copending patent application S.N. 464,578, filed on June 16, 1965 by F. H. Schwacke et al. It is intended to incorporate the disclosure of said application into the present application by reference. The copending application is directed to a new method for producing a leather substitute having a hand, breathability, scuff resistance, temperature resistance, crease resistance, tear resistance and an appearance very similar to that of leather. The method involves coating of a porous flexible base such as woven or non-Woven cotton with a coating of a breathable thermoplastic polyurethane coating.

While the coated fabric of the copending application has many of the desirable properties of leather and may be used as a leather substitute for many uses, We have found that when used as a shoe upper material, the coated fabric has less than the desired tensile strength and scuff resistance for such materials. We have found that the tensile strength and scuff resistance can be greatly increased while maintaining the breathability of the coated fabric with the desirable range for shoe uppers by compressing the blush coating on the fabric to from 40 to 60% of its original thickness.

This is accomplished through the application of heat and pressure. It is important that the coated substratev be preheated before the application of pressure. Preferably the coated substrate produced in accordance with the copending application is heated to a temperature in the range of from 195 to 300 F. and most preferably in the range of from 255 to 280 P. Then sufficient pressure is applied to reduce the thickness of the coating to from 40 to 60% of the original thickness. Such a reduction in thickness increases the tensile strength threefold. The preheating may be accomplished by any conventional expedient such as infrared radiation or heated rollers. The pressure may also be applied by conventional means such as calendering or embossing.

We have found that a threefold increase in tensile strength must necessarily be accompanied by a reduction in breathability as indicated by Moisture Vapor Transmission (M.V.T.). However, if the M.V.T. of the fabric is initially high e.g., above 2.0 g./ 10 cm. /24 hours, then the resulting M.V.T. after compression will still remain above 0.91 g./ 10 cm. 24 hours which is still substantially above the minimum M.V.T. of 0.5 g./10 cm. /24 hours set forth for the coated fabric of the copending application as well as the minimum M.V.T. for leather. (As described in the copending application, M.V.T. is determined as follows: The specimen under investigation is placed over the mouth of a Payne cup, which is circular and has an area of 10 square centimeters, so that it completely covers that mouth. The Payne cup contains 9 g. of 8 mesh calcium chloride granules. The covered cup is Weighed and then exposed for 24 hours to a relative humidity of The cup is weighed again after exposure and the gain in weight is noted. This gain in weight is the water vapor passing through 10 square centimeters in 24 hours. Thus, a specimen of leather which has passed 2 g. of water vapor in 24 hours, has a M.V.T. of 2 g./ 10 cm. /24 hours. The M.V.T. values for leather and for our new leather substitute which are set forth herein are determined by following that procedure.)

The blush coated fabric which is to be subjected to the compression step is prepared in accordance with the proce dure of the above-mentioned copending application.

The blushable coating may be applied to the base as a solution of the polyurethane in the volatile liquid mixture or as a colloidal dispersion of the polyurethane in such liquid, and the term uniformly distributed as used herein includes the solution state and the colloidal dispersion state of the polyurethane in the liquid.

Best results are achieved if the blushable coating is applied to the substrate at an elevated temperature.

The polyurethanes used in the practice of this invention are thermoplastic elastomeric polyurethanes which are essentially linear in character. They are prepared from long chain diols such as linear polyesters and polyethers having molecular Weights ranging from about 400 to 6000 and diisocyanates. The polyurethanes may also include in addition to the diols and diisocyanates, chain-extenders which are active hydrogen-containing difunctional compounds such as glycols, diamines, aminoalcohols and water.

The polyesters used in the preparation of the polyesterurethanes are prepared from the esterification of such dicarboxylic acids as adipic, succinic, pimelic, suberic, azelaic and sebacic or their anhydrides with glycols such as ethylene glycol, butanediol-1,4 hexamethylene-diol-l,6, and octamethylenediol-l,8. In general, the glycol has the the formula HO (CH )xOH with x preferably from 2 to 10.

The polyethers used in the preparation of the polyetherurethanes involved in this invention may be characterized by the formulation HO(RO) H where R is a divalent alkylene radical and n is preferably a positive integer such that the molecular weight of the polyether lies between 400 and 6000. These polyethers are conventionally known as polyalkyleneether glycols or hydroxyl poly(alkylene oxides). Some conventional polyethers which may be used are polyethyleneether glycol, polypropyleneether glycol, polytetramethyleneether glycol, polyhexamethyleneether glycol, polyoctamethyleneether glycol, polynonamethyleneether glycol, polydecamethyleneether glycol, polydodecarnethyleneether glycol and mixtures thereof. Polyglycols containing several different radicals in the molecular chain such as, for example the compound HO(CH OC H O),,H where n is an integer greater than 1 may also be used.

The solvent used in the blushable coating will depend on the polyurethane used as well as the nature of the non-solvent used since the solvent must be miscible with the non-solvent and must be more volatile than the nonsolvent. Once a solvent is selected, potential non-solvents will be readily determinable by those skilled in the art of blushed coatings. Pyridine, dimethyl formamide, dimethyl sulfoxide, pyrrolidones, cyclohexanone and preferably tetrahydrofuran and p-dioxane are suitable solvents for the polyesterurethanes and polyetherurethanes of Pats. 3,871,218 and 2,899,411 for example.

The selected non-solvent in the coating will depend on the polyurethane used and the nature of the solvent. The non-solvent must be a non-solvent for the polyurethane which is miscible with and less volatile than the solvent. While each of the following non-solvents will not be operable with each combination of solvent and polyurethane, they can be used in particular combinations: alkanols including butanol, hexanol and octanol, and aliphatic hydrocarbons particularly the aliphatic hydrocarbons with higher boiling ranges above 250 C. Of course, other non-solvents may be used, and these will be obvious to those skilled in the blushed coatings art.

While the base which we now prefer is a woven textile, non-woven textiles are utilizable. The term woven textile is meant to include knit textiles. Cotton textiles have produced good results. However, any of a wide variety of natural and synthetic textiles including textiles of mixed synthetic and natural fibers to which the coating will adhere firmly will give satisfactory results e.g., nylon, polyesters such as Dacron materials, materials of acrylics such as Orlon, vinyl chloride copolymers, cellulosics such as rayon and cellulose acetate as well as natural materials such as cotton, wool, ramie, hemp and linen. The blushable coating is preferably applied at a wet coating thickness of from 20 to 200 mils, and most preferably at a thickness of 140200 mils.

The polyurethanes used in this invention preferably have a molecular weight of from 5000 to 300,000 and most preferably from 40,000 to 80,000.

In the present specification and claims, all proportions are by weight unless otherwise set forth.

The following examples will further illustrate the practice of this invention:

EXAMPLE 1 A polyesterurethane having a molecular weight of about 60,000 is prepared following the procedure set forth in US. Pat. 2,871,218, col. 4, lines 13 to 27. A mixture of 1447 g. (1.704 mols) of hydroxyl poly(tetramethylene adipate), molecular weight 849, hydroxyl number 130.4, acid number 0.89, and 109.6 g. (1.218 mols) of butanediol-1,4- is melted in a four liter kettle and stirred with a spiral ribbon stirrer for about 20 minutes at a pressure of 5 to 6 mm. at 100 to 110 C. To this mixture, there is added 730 g. (2.92 mols) of diphenyl methane-p,p diisocyanate. This mixture is stirred for about 1 minute and is then poured into a lubricated one gallon can which is promptly sealed with a friction top and the can placed in a 140 C. oven for 3.5 hours. The product is then cooled. A 20% solution of the polyesterurethane in p-dioxane is prepared.

Then 150 g. of the solution are heated to and maintained at 90-92 C. While 110 cc. of n-hexanol are added slowly. The solution is clear. The mixture is then slowly cooled until opalescence appears at 42 C. The opalescent composition is then cooled another 5 C. and coated at a thickness of inch onto the surface of a cotton sheet having a weight of 0.002 ounce per square inch and airdried for a period of 16 hours at room temperature. The coated surface has a hand closely resembling that of a leather, excellent scuff and abrasion resistance if the coated fabric is to be used as a leather substitute in coats and jackets and a moisture vapor transmission or breathability equal to that of leather.

The coated fabric of this invention passed 3.4 g. of water vapor in 24 hours. The M.V.T. of the fabric may be set forth as 3.4 g./ cm. /24 hours as compared to leather which has an M.V.T. of 0.5 to 3.5 g./ 10 cm. /24 hours.

The coated fabric has a tensile strength of about 500 lbs. per square inch. While the coated fabric has a scuff resistance and tensile strength equivalent to some types of leather, these properties are found to be less than fully desirable if the coated fabric is to be used in shoe uppers. If so used, the coated fabric is too easily scuffed and marred. In order to overcome this deficiency, the coated fabric is heated by being passed through two sets of rollers at 275 F. The nip between the respective sets of rollers being sufiicient so that there is no reduction in coating thickness. Then the heated coated fabric is passed through a set of rollers having a nip of 0.03 inch. The original substrate has a thickness of 0.022 inch and the coating a thickness of 0.048 inch.

The resulting compressed coating has a thickness of 0.024 inch which is 50% of the original thickness. The breathability of the coated fabric is 2 g./ 10 cm. 24 hours which is very good for shoe uppers. The tensile strength of the coated fabric is increased threefold to 1500 lbs. per square inch. The coated fabric may be readily used in shoe uppers in which it displays minimal scuffing and marring.

EXAMPLE 2 40 g. of a polyetherurethane prepared from hydroxyl poly (tetramethylene oxide), diphenyl methane-p,p-diisocyanate and butanediol -l,4 in accordance with the procedure set forth in US. Pat. 2,899,411, Example III are dissolved in 160 g. of p-dioxane. The solution is then heated to 95 C. and maintained at C. to C. while 57.1 g. of an alkane hydrocarbon solvent having a boiling range of 350-388 F., a K.B. value of 27 and an aniline cloud point of 184.5 F. are added over a period of 12 minutes with continuous stirring. A solution which is clear to the eye forms. The solution is cooled. At 42 C., the solution becomes opalescent. The composition is permitted to cool to 39 C. The composition is then coated at a thickness of j inch onto the surface of a cotton sheet having a weight of 0.002 ounce per square inch and air-dried for a period of 16 hours at room temperature. Alternatively, the coating may be air-dried for about 1% hours at room temperature and then for 2 hours at 65 C. After drying the coating has a thickness of about inch and a hand closely resembling that of a leather.

The coated fabric of this example passed 1.9 g. of water vapor in 24 hours. The M.V.T. of the fabric may be set forth as 1.9 g./10 cm. /24 hours as compared to leather which has an M.V.T. of 0.5 to 3.5 g./l0 cm. /24 hours depending upon the type of leather.

However, the coated fabric displays the same less than desirable scuff resistance and tensile strength as does the coated fabric of Example 1 when used in shoe uppers.

When the procedure of Example 1 is then repeated to compress the coating to 50% of its original thickness, the resulting coated fabric has the same desirable sculf re sistance and tensile strength for shoe uppers as does the compressed coated fabric of Example 1.

While there have been described what is at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. In the method of applying a water vapor permeable coating onto a porous flexible base comprising covering a surface of said base with a coating comprising a thermoplastic elastomeric polyurethane uniformly distributed in a mixture of a volatile solvent for said polyurethane and a volatile liquid miscible with said solvent which liquid is a non-solvent for said polyurethane and is less volatile than said solvent and removing substantially all of the volatile mixture by evaporation, the improvement which comprises heating the coated base after removal of the solvent to a p ature of at least C. and then applying suflicient pressure to the heated coated surface to reduce the thickness of the coating to from 40 to 60% of the original thickness.

2. The method of claim 1 wherein the coated base has a moisture vapor transmission of at least 2.0 g./ 10 cm. 24 hours.

3. The method of claim 2 wherein the heated base is calendered to reduce the coating thickness.

4. The method of claim 3 wherein the base is heated by being passed over heated rollers.

5. The method of claim 1 wherein said urethane is a polyesterurethane.

6. The method of claim 5 wherein said polyesterurethane is an essentially linear polyesterurethane elastomer which is the reaction product obtained by heating a mixture comprising as essential polyurethane ingredients (1) one mol of an essentially linear hydroxyl terminated polyester of a saturated aliphatic glycol having from 4 to carbon atoms and having hydroxyl groups on its terminal carbon atoms and a material selected from the group consisting of a dicarboxylic acid of the formula Where R is an alkylene radical containing from 2 to 8 carbon atoms and its anhydride, said polyester having an average molecular Weight between 600 and 1200 and having an acid number less than 10, and (2) from 1.1 to 3.1 mols of a diphenyl diisocyanate having an isocyanate group on each phenyl nucleus in the presence of (3) from about 0.1 to 2.1 mols of a saturated aliphatic free glycol containing from 4 to 10 carbon atoms and having hydroxyl groups on its terminal carbon atoms, the molar amount of said polyester and said free glycol combined being essentially equivalent to the molar amount of said diphenyl diisocyanates whereby there are essentially no groups of the class consisting of isocyanate and hydroxyl groups in said reaction products.

7. The method of claim 6 wherein said polyesterurethane is a linear hydroxyl terminated polyester produced by the reaction of hydroxyl polytetramethylene adipate and butanediol-1,4, and said diisocyanate is diphenyl methane-p,p' diisocyanate.

References Cited UNITED STATES PATENTS 3,100,721 8/1963 Holden ll7135.5 3,180,853 4/1965 Peters 117l61X 3,238,055 3/1966 Brightwell 1l765.2

WILLIAM D. MARTIN, Primary Examiner T. G. DAVIS, Assistant Examiner US. Cl. X.R. 117135.5, 161 

